3rd. System V IPC

3.1 Overview

System V IPC Functions:

3.2 key_t and Ftok functions

Key_t is the external identifier of the system V IPC, also known as the IPC Key, through which multiple processes meet on the same IPC object

The Ftok function converts pathname and integer identifiers to key_t values

#include <sys/ipc.h>key_t ftok (char *pathname,int ID)

Client and server agree on pathname and ID, then both sides get the same IPC key by calling the Ftok function

Three get functions (Msgget, Semget, shmget) use the key and flag parameters to create or get an IPC object that returns an int type identifier

A) Key=ipc_private is created

b) key is not associated with an IPC object and the specified ipc_creat bit in flag is created

3.3 Ipc_perm Structure

struct ipc_perm{        uid_t   uid;        gid_t   GID;        uid_t   cuid;        gid_t   Cgid;        mode_t  mode;        ulong_t Sep;        key_t   Key;};

3.4 Creating and opening IPC channels

From the IPC key to the IPC identifier:

To open a logical process for an IPC object:

3rd. System V IPC